Control apparatus



Oct. 12, 1948. R. D. COWHERD 2,451,073

" CONTROL APPARATUS Filed June 22. 1944 l2 ll. l2 NoaMALLY OPEN I l8 l7 I ll STEAM NORMALLY CLOSED I2 ll l2 0 o o o o o 0 0 0 o o o 0 o o 0 0 O O O O 00 T: 20 o o o o o 0 0 l o o o o o o 0 0 o 0 o o o o o 50 o o o o o o o I 22 STEAM INVENTOR.

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Patented Oct. 12, 1948 umrrr-zp STATES PATENT OFFICE Robert D. Oowherd, Atlanta, Ga., alaignor to The Bristol Company, Waterbury, Conn, a corpora- I lion of Connecticut Application June 22, 1944', Serial No. 541,613

8 Clahna. (Cl. 210-452) This invention" relates to automaticcontrol in the operation of processing apparatus wherein it is desirable to prevent solid or semi-solid material from entering a conduit or a pipe line or a reaction vessel whose content is normally restricted to fluid media. The invention has been developed in conlunction with the control or the operation oi'a pulp-disaster, in the manufacture of paper. and will hence be here illustrated and described as applied thereto: although it will be -apparent that its utility is not restricted to any particular apparatus.

In the manufacture of wood pulp it is customary to charge a closed vessel known as a .digester with a quantity oi wood chips and suitable chemicals and then .to set up a reactionby the admission oi steam or other heating a ent.

' In the course of this process, certain gases are given oil; and it is usual to vent these from the top of the digester in a manner to maintain predetermined pressure values within the disester.

Due to the chemical characteristics of the solution or liquor within the digester there is a tendencytoward foaming, with the result that under certain conditions some oi the solution may be drawn oi! with the gas, carrying with it masses of solid or semi-solid material, thus not only depieting the content of the digester but introducing conditions which may be responsible for clogging or otherwise in'teriering with the proper lune-,-

tloning of auxiliary apparatus.-

Automatlc control oi the venting of gases is not new; and it is customary to equip d sesters with instrumentalities which will realllate a valve in the vent pipe in accordance with predetermined pressure settings. Such devices, however, take no cognizance of the condition of the fluid. being vented, and will as readily vent the digesting liquor as' ihe gaseous products of the reaction. An e'iiectlve means oi discriminating between liqing system is prevented, and none but fluid materials allowed to pass. Under certain conditions of operation, there may accumulate upon" the screen such a quantity oi pulp or chips or'mixtures oi the same. as to obstruct the flow therethrough of the normal eiiiuent. thus seriously interfering with the proper operation or thedigcster.

It is an object or this present invention to provide means whereby a strainer in the path of fluid flow in an apparatus may be cleansed oi obstrueting material without interfering with the operation of the apparatus.

It is a further object to provide means whereby the cleansing operation may be renderedwholly automatic, not normally requiring the superposition of manual control.

The invention also comprises means responsive to a pressure diflerential onopposite sides of the strainer for controlling the application 01' a purging fluid to the strainer.

A iurther object is to control the duration of the flow oi purging liquid.

The invention also provides for interrupting the normal flow oi fluid from the apparatus during the application of purging liquid to the screen.

A more specific object comprises superimposing upon such automatic regulating devices as may normally characterize a digester system. a control system whereby, upon the development of an abnormal pressure drop across the strainer or screen due to clogging thereof by solid or semisolid matter accumulated thereon, there will be actuated instrumentalities to introduce a purging cycle, wherein the normal venting oi eilluent from the digester will be temporarily halted, and a jet oi steam or other suitable purging fluid admituid and gaseous phases in the eilluent is fully described and set forth in my co-pending application for U. 8. Letters Patent, Serial No. 448,895, flied May 21, 1942, now Patent Number 2,411,986,

dated December 3, 1946; Because there is likelyv to exist in pulp digesters a certain degree of turbulence, causing masses of partially digested wood pul to be thrown up into the eilluent line, it is customary to provide a strainer or screen, by which the passage of this material into the pipthe digester shown in Fig. 1 and showing certain detailsbf construction thereof.

Referring now to the drawings, the numeral ll designates a pulp-digester into which mixture of wood chips and suitable chemicals may be charged through an opening in the top, which is afterwards sealed by a cover plate Ii secured in place by means of bolts II. A conduit i3 provides for the admission of steam to the lower part of the digester. A conduit ll connected near the top of the digester provides for the venting of products of the internal reaction to the atmosphere, or to a receptacle not shown in the drawings whereby certain valuable constituents of said products may be salvaged. The venting of said products is regulated bya diaphragm valve ill inserted in the conduit i4 and subject to actuation by air admitted to its operating element through a conduit i6. Said valve is is shown as of the "directacting" type, its action being such that it normally stands open, and increase of pressure in the conduit i6 tends to move its internal parts to a closed position. A pipe I! provides for the admission of steam or other suitable flushing agent to the conduit i4, whereby the same may be admitted to the upper part of the digester to impinge upon internal parts presently to be set forth. A diaphragm valve IQ of the reverse-acting type is inserted in the pipe", and has its operating element placed in communication with the conduit ii, whereby air pressure within said conduit will cause said valve to be opened.

, The interior construction of the upper portion of the pulp digester ill will be better understood by reference to Fig. 2. Secured to the inner surface of the cover plate ii is a cylindrical strainer or screen 20 formed of perforated metal or the like, said screen projecting downwards into the upper part of the digester and being surrounded by an inwardly directed flange member 2i attached to the inner surface of the digester, whereby there is formed about the screen 20 an annular chamber 22 communicating directly with the vent pipe II and with the interior of the digester only through the perforations in the screen 20. The perforations in the screen 20 are so dimensioned and spaced as to prevent the passage of chips or other solid or semi-solid masses,

while at the same time allowing egress of fluid efliuent from the space within the digester to the annular chamber 22, and thence to the vent pipe i4. Under normal operating conditions the total area represented by the perforations in the screen 20 will be suflicient to allow free passage of effluent from the digester II to the vent pipe ll with a negligible pressure. differential across the screen; but upon said perforations becoming obstructed by chips or other solid or semi-solid matter, the consequent reduction ineffective cross-section area of opening will cause a pressure differential to be developed; and it is this differential which it is proposed to utilize for the purpose of actuating control apparatus whereby to purge or flush the screen of undesirable obstruction.

Connected to the body of the digester II, and in free communication with the interior thereof, is a conduit 28; and a similar conduit 24 is connected to the vent pipe ll, whereby to be subjected to the pressure existing within said pipe. Referring again to Fig. 1, a pneumatically operated three-way valve and a pressure-differentialresponsive electrical contactor 26 are provided, and are interconnected in the following manner: The conduit 23 is connected to one side of thecontactor 2i. and the other side of said contactor is connected by means of a conduit 21 to the three-way valve ll. The valve II is also connected to the conduits 23 and 24 in such a manner that when no pressure is present in the operating element of said valve the conduits II and 21 will be in mutual communication, and

both cut oil from the conduit II. When air pressure is applied to the operating element of the valve II, the position of its interior parts will be so changed that conduits II and 21 will be placed in mutual communication and both cut of! from conduit 24. The operating element of the valve 28 is connectedetothe conduit ll, whereby, when pressure is applied to said conduit all three of the valves II, ll and 2| will be operated in unison.

The contactor 26 is provided with contact elements 2! adapted to be interconnected when the pressure in the side of the contactor connectedto the conduit 23 exceeds by a predetermined amountthat in the side of the contactor conelement 32 is provided with normally closed coni tacts, and also with a timing element 13, whereby, upon energization of its actuating coil, there will be initiated a delay interval as established by said timing element, after which interval the normally closed contacts of said relay will be b im, t e'relay opened.

Devices incorporating the member 30 are well-known to those versed in the art of electrical control; and an example of a relay thus adapted to the purposes of the invention is found in Patent No. 2,175,864, granted to C. L. Anderson, October 10, 1939.

A three-way solenoid-actuated valve II is connected in the conduit it in such a manner that. when the actuating coil of said valve is energized,' air pressure from a source it will be applied to the conduit ii, and when said coil is deenergized, the conduit II will be placed in communication with the atmosphere through a vent 31, and cut oil from the supply 38.

The electrical elements of the control system are interconnected in the following manner: A suitable source of electrical energy is represented by two conductors l0 and I. The conductor ii is connected to one side of the contact element ll in the contactor ii, and also to one side ating coils of relay elements fl and If and solenoid valve 3!, and also of contact element It. The free terminals of the contacts of relay elements I1 and I2 are interconnected by means of a conductor 43.

The functioning of the apparatus involving" the principles of the invention is as follows: Assuming all connections to be made as hereinbefore described, and the digester to be operating normally, without any material degree of obstruction in the screen 23', whereby to build up a pressure gradient across the same, there will be substantially no pressure diflerential in the contactor 23, and the contacts 23 of the same will stand in an open position. The contacts of the relay 3i being opened, there will be no complete circuit in the electrical network of the apparatus, and the relay 3! will remain de-energized, as well as the relay 32 and the solenoid valve 33. The conduit i3, and the actuating elements of the three pneumatically operated valves connected thereto, will thus be placed in communication with the atmosphere through the vent 31 and isolated from the air supply 33. Consequently, the valve 25 will stand with conduits 23 and 21 in mutual communication, and both out of! from the conduit 23. Valve is will stand in its open position, allowing free venting of the eilluent from the digester, and valve l3 will stand in a closed position, preventing steam in the conduit II from entering the pipe l4. Since the pressures in conduits 23 and 21 are substantially of a common value said pressures applied to the contactor 26 will produce no diilerential action, and the contacts 23 will remain opened.

It may now be assumed that, in the course of operation of the digester, the screen 23, performing its normal function 01' excluding solid and semi-solid material from the vent pipe l4, has become clogged with chips and the like to an extent that the effective area of the openings through said screen is materially reduced, thereby causing the pressure in the annular chamber 22 to become materially less than that within the interior of the digester. The pressure gradient across the screen 23 will appear as a diflerential between the pressures in the conduits 23 and 24; and since the latter of said conduits is directly in communication through the valve 23 with conduit I'Lsaid pressure diflerential will be applied to the contactor 23. When the excess of pressure in the conduit 23 over that in conduit 21 attains a value corresponding to the setting of the contactor 23, its contacts will be closed. There will thus be provided a path between conductors 43 and 32, whereby current may flow between conductors 49 and 4| through the windings of relays 3| and 22 and the actuating coil of valve 33 in parallel, thereby energizing all three of said windings. of the winding of the valve 33 will cause conduit it to be cut of! from connection with the vent 31 and placed in communication with the air supply 36, whereby pressure will be applied to the actuating elements of valve 23, i3, and I3. Operation of the valve 23 will cause conduits 23 and 21 to be'placed in communication with each other and cut on from conduit 24. Thus, the two sides of contactor 26 will both be subjected to pressure existing in the conduit 23, whereby, there no longer being any differential between the two sides of the pressure-sensitive element of said contactor, the contacts 23 will be opened. Relay 3i being energized, however, there will be provided through its contacts and the normally closed contacts of relay 32 an alternative path,

whereby the windings of said relays, as well as that of the valve 35. will remain energized after the opening of contacts 23. Air pressure applied to the operating element of the valve II will cause it to be closed, thus stopping the venting of eilluent from the digester through the pipe l4, and allowing the pressures in the interior oi the digester and in the annular space 22 surroundvalve l3 will cause said valve to be opened and a jet of steam from the conduit l1 admitted to the pipe i4. and thereby to the chamber 22, thus building up a pressure in the space 22 exterior to the screen 23, and introducing a purging cycle, in which any obstructing material which in have accumulated on the inner surface, or within the openings, of said screen is blown back into the digester.

The purge. duringwhich steam is admitted to the digester from the conduit I! will continue so long as the valve 33 remains energized; which will be until the efectric circuit to the actuating winding of said valve is interrupted by opening oi the normally closed contacts of relay 32. The duration oi the purging cycle will thus represent the interval established by timing element 33 ot the relay 32, which introduces a predetermined delay between the energization of said relay and the opening of its normally closed contacts. This time interval would normally be made adjustable by means incorporated in the relay mechanism. and not taming a part of the present invention. Such means are fully described and set forth in the aforesaid Anderson Patent No. 2,175,864.

. Upon'opening of the contacts of the relay 32, the

supply 0! current to the winding of the valve 33 duit [1 to the interior or the digester; and the valve II will be opened, allowing normal venting of the eilluent again to be established. Valve 23 will revert to its normal condition, whereby the differential pressure across the screen 23 within the digester is applied to the contactor 23.

It the purging cycle has been effective in clear- I ing the screen 23 of obstructing material, the

Energization pressure gradient across said screen will-have disappeared or fallen to'a value below the setting oi the contactor 23, so that its contacts 23 will remain open, with the result that normal operation of the digester will be continued. In the event that the purging action has not been continued tor a sumciently long time, or if for any other reason the screen has not been eil'ectively cleared, a pressure gradient will again be built up across said screen. actuating the contactor 23, and causing the cycle as hereinbei'ore described to be repeated. It the cycle should continue to repeat indefinitely it will be apparent to the operator in charge that there has developed an undesirable condition requiring special attention and the pos-- 'sible superposition of manual control or other non-automatic influences until normal action is re-established.

If desired, there may be connected, in parallel with the relays 3i, 32 and solenoid valve 33. an electric hell or light 43 for providing a signal at any desired point to apprise an" attendant that the purging apparatus is in operation.

The apparatus embodying the principle of the present invention may be used in conjunction with. or independently of, the liquid-gas-phase control described and set forth in my co-pending application Serial No. 448,895, filed May 21, 1942, now Patent Number 2,411,986 above referred to; and the extent to which valves and other control instrumentalities may be made common to both elements or the installation will be obvious to earners the manufacture of wood pulp and in kindred The terms and expressions which I have emj ployed are used as terms or descriptionand not of limitation, and I have no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but recognize that various modifications are possible within the scope of the invention claimed.

I claim: 1

1.- Apparatus for removing obstructing material lrom a strainer mounted in a container for a flowing fluid, said apparatus comprising diflerential pressure responsive means having conduit means for connection to said container on opposite sides of said strainer to respond to the pressure diflerential thereacross, valve means for controlling the flow of a purging fluid through said strainer,

'tlmed relay means connected to said pressure responsive means for operation in response to the attainment of a'predeter'mined pressure diflerential across said strainer, connections between said relay means and said valve means and controlled by said relay means for actuating said valve means to establish said flow of purging fluid for a predetermined interval, together with further valve means operable to connect oppositesides or, said pressure responsive means to the pressure on only one side of said strainer, and connections controlled by said relay means for eflecting actuation of said further valve means coincidentally with said first valve means to connect said opposite sides of said pressure responsive means to said pressure on only one side of said strainer during said interval.

2. Apparatus for removing obstructing material from a strainer mounted in a container for a flowing fluid, said apparatus comprising diflerential pressure responsive means having conduit means for connection to said container on opposite sides of said strainer torespond to the pressure diflerential thereacross, valve means for interrupting the flow of said fluid, other valve means for controlling the flow of a purging fluid through said mentioned fluid and establish flow of said purgtion of said third valve means coincidentally with the other valve means for applying to opposite sides of said pressure responsive means the pressure on only oneside of said strainer.

3. Apparatus for removing obstructing material from a strainer mounted in a container for a flowing fluid, said apparatus comprising normally closed valve means for controlling the flow through said screen of a purging fluid different from the first mentioned fluid, control 'means for said valve means comprising a difierential-fluidpressure responsive element, conduit means for connecting opposite sides of said element to said container on opposite sides "of said strainer for subjecting said element to corresponding fluid pressures, electrical switch means mechanically said strainer, means for operatingsaid valve means, and electrical connections controlled by said switch means for controlling said operating means for opening said valve means to admit purging fluid to said screen pursuant to attainment. of said pressure diflerential.

4. In combination with a processing vessel having a vent pipe for the escape of fluid therefrom and a strainer in saidvessel adjacent said vent pipe to separate entrained matter from said fluid, a valve in said vent pipe normally opened and adapted to be closed to prevent the outflow of said fluid, means for supplying steam to said strainer for purging the latter of accumulated suspended matter, a valve normally closed and controlling .the admission of said steam to, said strainer, a fluid-pressure responsive element, conduit means for connecting opposite sides of said element to said vessel on opposite sides oi said strainer for subjecting said element to corresponding fluid pressures, electrical switch means mechanically connected to said fluid pressure responsive element for operation in response to attainment of a predetermined pressure difl'erential across said strainer, means for operating said valves in'opposite senses, and electrical connections controlled by said switch means for controlling said valve operating means to close the first-mentioned valve and open the second mentioned valve in response to attainment of said pressure differential.

5. In combination with a processing vessel having a vent pipe for the escape of fluid therefrom normal flow therethrough, whereby to clear the same of accumulated suspended matter, a fluidpressure responsive element, conduit means for connecting opposite sides of said element to said vessel on opposite sides of said strainer for subnected to said fluid-pressure responsive element for operation in response to attainment of a predetermined pressure differential across said strainer, a third valve connected to the pressure applying means for said pressure-responsive'element and operable to establish communication between opposite sides of said element, and connections between said switch means and all of said valves for operating the latter in response to attainment of said pressure diilerential.

6. In combination with a processing vessel having a vent pipe for the escape of fluid therefrom and a strainer in said vessel adjacent said vent pipe to separate entrained matter from said fluid, a valve in said vent pipe normally opened and adapted to be closed to prevent the outflow of said fluid, means for supplying steam to said strainer for purging the latter of accumulated suspended matter, a valve normally closed and controlling the admission of said steam to said strainer, a fluid-pressure responsive element, conduit means for connecting opposite sides of said element to said vessel on opposite sides of said strainer for subjecting said element to corresponding fluid pressures, electrical switch means mechanically connected to said fluid-pressure responsive element for operation in response to attainment of a predetermined pressure differential 9 across said strainer, means for operating said valves substantially simultaneously in opposite senses, a source of electric power, and connections from said source controlled by said switch means for controlling said valve operating means to close the first-mentioned valve and open the second mentioned valve in response to attainment of said pressure differential.

ROBERT D. COWHERD.

REFERENCES CITED UNITED STATES PATENTS Name Date Lindsley Feb. 24, 1885 Number Number 10 Name Date Paterson Aug; 14, 1900 Genter Apr. 16, 1918 Tompkins June 5, 1923 Martin et a1 Oct. 18, 1932 Christensen Mar. 31, 193B MacIsaac Jan. 5, 1937 Haught June 22, 1937 -I-Iaught May 31, 1938 Anderson Oct. 10, 1939 Hughes Dec. 12, 1939 Dunbar June 18,- 1940 Huxford July 16, 1940 Harms -1 Jan. 9, 1945 Cowherd Dec. 4, 1946 

